1. Field of the Invention
The invention concerns a special process and a corresponding device for preferably machining production of workpieces with unround inner and/or outer contours, in particular eccentrically positioned round boreholes and/or journals. Unround contours such as, for example, squares, hexagons, ovals, ellipses or polygons as bore holes or on journals are necessary in the industry for the most diverse applications and in the most varied geometries. Generally known and broadly utilized are, for example, internal hexagons in the heads of screws. For the machining of such screws one could consider essentially shaping processes such as, for example, cold- or warm-press extrusion, since with these processes it is possible to produce pieces with a useable outer surface and at the lowest possible cost per unit. The situation is different when a smaller number of parts are required, or when the respective component cannot be produced by this type of press extrusion process. Above all in the general machine construction industry there is a need for the most varied borehole shapes or, as the case may be, outer contours, and for the machining production of components. Here, with respect to inner contours, resort is conventionally made to broaching or trimming, in some cases also to erosion, or form boring by means of a template, while for the production of outer contours conventionally consideration is given to milling or cutting production.
In the broaching or trimming of shaped boreholes, also in the case of pendulum broaching, this is generally resulting in a more or less strongly grooved surface of the form borehole. The accuracy to gauge or size a borehole produced in this manner is moderate. In the case of harder working materials a higher wearing away of the broaching needle occurs. Additionally, in the case of pocket or dead-end boreholes, there is the disadvantage of the occurrence of trapped metal shavings.
The erosion of form boreholes leads to excellent results, even in hardened materials. However, the time requirement for this type of production is very high, so that this process can in most cases be taken out of consideration due to high costs.
On the other hand, an apparatus for rotative cutting or milling production of form boreholes is known, which is produced by the company VIKA AG in Trimbach, Switzerland, and is sold under the name VIKA-Polybor. This device is essentially comprised of a special borer, which by means of a floating holder can be clamped into a machine spindle and which during the drilling process is guided with the respective desired contour via a hardened template associated with the workpiece. The function of this device is however deficient in the respect that its applicability is very limited. A fundamental disadvantage of this device is the fact that already for geometric reasons a multi-angled drill cannot describe a distinct path within the template, so that the produced contour departs from the contour of the template in a variable manner. Due to the impacting during rotation the outer border edges will, over time, be rounded off in such a manner that in the front side regrinding of the drill the inner measurements of the bore to be produced become smaller and the drill becomes loose in the template. The drill made of HSS is not only expensive to purchase and difficult to regrind, but rather also possesses a particularly impractical or undesirable cutting edge geometry. A fitting or mounting of exchangeable cutting inserts is not possible. It is a further disadvantage, that prior to beginning of the drilling operation the template must be mounted above the workpiece, and the borer must first be introduced into the template with a resting or non-moving spindle, so that a particularly inconvenient manner of operation is produced, which for example cannot be carried out upon an automatic operating machine.
With respect to the cutting production of outer contours today a number of technical possibilities are available, of which milling might be considered to be the closest. However, milling is known to have a small cutting capability per unit of time in comparison to turning. Here special devices are also known such as, for example, the so called multi-edge cutting devices, which produce quite good results with milling machines. This type of multi-edge milling machines however do not permit the production of rounded contours such as, for example, ellipses or three-lobed shapes, and are not usable for example on a CNC lathe with driven tools.
2. Description of the Related Art
A form drilling or form turning device is known from EP-PS 0 513 322, which is suitable for the cutting production of a large number of the most diverse inner and outer contours. This device has the advantage, that it can be mounted upon lathes as well as milling machines, and can even be mounted on column type drilling machines, wherein there is essentially only the need for a rotational drive for the device itself. Thus, even also larger workpieces with higher weight, which for example must be mounted securely upon the work table of a milling machine, can be processed without problem. It can further be employed with lathes which have neither a mechanical nor electronic coupling between the spindle and work tool driver, but rather essentially take advantage of the availability of the spindle-stop or brake. On the other hand, it is a disadvantage of this device, that for each different geometric form or shape and also size a different cam disk set is necessary, from which there follows an increase in investment costs and a corresponding time requirement for equipment change-over. It is further disadvantageous, that without external adjustment of the cutting insert neither an incrementally split-up chipping nor a calibration of the contour can be carried out.
Besides this, from European Patent Document 0 097 346 two principle processes and various devices for the cutting production of this type of contours are known. In the one proposed device the workpiece as well as also the work tool rotate upon a circular path with speeds of rotation differing from each other, wherein the rotating axis of the work tool is displaced eccentrically against the rotating axis of the workpiece. Therewith, by means of a special uneven transmitting driving unit, the rotational speed of the work tool is influenced in such a manner, that from the relative movement between the work tool and workpiece the desired unround contour is produced. Besides this, by means of a predetermined respective radial axis displacement between the workpiece and work tool, the diameter difference between inner and outer circumference of the contour is fixedly established (the term "inner circumference" referring to the radial distance from the workpiece axis of rotation to the nearest machined point on the workpiece; the term "outer circumference" referring to the radial distance from the workpiece axis of rotation to the furthest machined point on the workpiece), just as from the rotation number relationship of the rotating partners the number of edges is determined. Therewith however there is associated the serious disadvantage, that the entire contour must be produced in one single cut. That is, when the work tool unit is moved radially relative to the workpiece, this leads essentially to either a formation of sharply pointed edges or rounding off of the edges of the contour, so that a fine adjustment of the diameter or a segregation into multiple cuts in this way is not possible. From this there results that in part very thick cutting chips are produced, from which not only a frequent breaking of the work tool must be expected but rather also an unclean or unsmooth processing surface. Beyond this, it is necessary for each dimension of the contour, to newly set or adjust the cutting tip or, as the case may be, to exchange the work tool holder or the drill rod with the drill bit, in order that an exact cutting-tip position can be maintained.
In the second process proposed in the same patent document, a workpiece is likewise rotated, the work tool however without its own rotation moves with its tip along a circular orbit lying outside the center of the workpiece, wherein the diameter of this circular path corresponds to the radius difference between the inner and the outer circumference of the contour. Here also uneven speed changes of drive steps are used to produce a variation of the orbiting speed of the work tool, with the relative movement between the workpiece and work tool determined so that during the processing the desired contour is produced. As before, by means of the driven steps a certain transmission ratio can be established herein with respect to the number of edges of the contour which in this case corresponds to the numeric ratio between the workpiece rotation and the work tool orbits. In the proposed process there is the disadvantage, that by the feed of the orbiting work tool tip along a helix lying upon a single circular cylinder neither a split-up chipping nor a calibration during the production of the contour is possible.
The devices proposed in the above document for carrying out of the later process are relatively expensive and require a particular construction size which already approaches that of a special machine. Significantly more versatile would however be a construction embodiment in the form of a work tool unit which is compact and machine mountable, such as, for example, on a lathe. In this respect the complex construction of the proposed uneven transmitting drive is certainly an obstacle. Further of disadvantage are the proposed technical solutions for the bearing of the torque or rotation moment forces of the oscillating head in the machine. The embodiment with the illustrated parallel hubs does not make possible a defined angular orientation or positioning of the oscillating head, which would be necessary for an orderly function. The embodiment with pivot arm and linear guidance is not practicable, since in the case of inexact positioning of the work tool cutting edge it causes a distortion of the profile or contour shape and influences the cutting angle of the workpiece cutter. Besides this the bearings for supporting the rotation moment forces described in the reference are not designed to bear the axial forces which occur during cutting or milling.
Thus, there arose the task of providing an improved process and an improved device for the preferably machining production of the contours, which were given above by way of example, on workpieces with increased requirements on the cleanliness or smoothness of the outer surface and the dimensional accuracy of the contour, without the above described disadvantages. Besides this, this type of device should function exceptionally economically and preferably be capable of being installed as after-market compact work tool units upon machines, above all lathes.
The described task is inventively accomplished by the provision.